In computer networking, the localhost (meaning this computer) is the standard hostname given to the address of a loopback network interface. On modern computer systems, the localhost as a hostname translates to an IPv4 address in the 127.0.0.0/8 (loopback) net block, usually 127.0.0.1.
Localhost is specified where one would otherwise use the hostname of a computer. For example, directing a web browser installed on a system running an HTTP server to the Uniform Resource Locator (URL) of http://localhost will display the home page of the local website, provided the server is configured to service the loopback interface.
Using the loopback interface is useful for testing software, such as web based applications, since it bypasses local network interface hardware. Connecting to locally hosted network services using loopback addresses puts less of a load on network resources.
While using the loopback interface is useful for testing software, the developer of the software may want to share in an electronic communication (e.g., e-mail, instant message) the URL that specifies the location of the application on the local machine. However, in order for other users to retrieve the application via the use of the URL, the localhost in the URL needs to be replaced with either the fully qualified domain name or the Internet Protocol (IP) address of the machine that is hosting the application.
Currently, in order to communicate the appropriate URL to the other users to retrieve the application hosted on the developer's machine, the developer manually copies the URL from his/her browser and replaces the localhost with either the fully qualified domain name or the Internet Protocol (IP) address of the machine that is hosting the application. However, such a process leads to errors, such as when the developer incorrectly copies and pastes the URL into a communication (e.g., e-mail) to another user or incorrectly types the domain name/IP address that replaces the localhost in the URL.